Add stats collection for telemetry startup.warm.blank_page test.

mojo/services/tracing/tracing.mojom

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 module tracing;
 
 // To participate in the tracing ecosystem, implement the TraceController
 // interface and connect to the tracing app. Then, when the controller's Start()
 // function is called collect tracing data and pass it back via the provided
 // TraceDataCollector interface up until Stop() is called.
 
 interface TraceController {
   StartTracing(string categories, TraceDataCollector collector);
   StopTracing();
 };
 
 interface TraceDataCollector {
   DataCollected(string json);
 };
 
 interface TraceCoordinator {
   // Request tracing data from all connected TraceControllers to stream to
   // |stream|.
   Start(handle<data_pipe_producer> stream, string categories);
 
   // Stop tracing and flush results to file.
   StopAndFlush();
 };
+
+// These times are used to determine startup performance metrics.
+struct StartupPerformanceTimes {
+  // TODO(msw): Rename to match "BrowserMainEntryTimeAbsolute" metric?
+  int64 shell_process_creation_time;

[sky, 2015/08/12 23:54:36]

Again, I think all this should be timeticks, not times.

[msw, 2015/08/14 23:20:35]

I filed http://crbug.com/521164 for this and added TODOs.

+  int64 browser_message_loop_start_time;
+  int64 browser_window_display_time;
+  int64 browser_open_tabs_time;
+  // TODO(msw): Rename to avoid "web contents"?
+  int64 first_web_contents_main_frame_load_time;
+  // TODO(msw): Rename to match "FirstWebContents.NonEmptyPaint" metric?
+  int64 first_visually_non_empty_layout_time;
+};
+
+interface StartupPerformanceController {

[yzshen1, 2015/08/13 15:59:12]

'Controller' seems a little confusing. Because Trace'Controller' above is an
interface implemented by clients of the tracing app.
StartupPerformance'Controller', on the other hand, is implemented by the tracing
app.

This interface is more like the TraceDataCollector above. Maybe it should be
called StartupPerformanceDataCollector?

[msw, 2015/08/14 23:20:35]

I went with StartupPerformanceDataCollector, but it's a long name; other
suggestions are welcome.

[yzshen1, 2015/08/17 05:46:38]

(Optional) One idea is "Performance" -> "Perf". So it is
StartupPerfDataCollector.

+  // These setters may be called many times, only the first call is recorded.
+  SetShellProcessCreationTime(int64 time);
+  SetBrowserMessageLoopStartTime(int64 time);
+  SetBrowserWindowDisplayTime(int64 time);
+  SetBrowserOpenTabsTime(int64 time);
+  SetFirstWebContentsMainFrameLoadTime(int64 time);
+  SetFirstVisuallyNonEmptyLayoutTime(int64 time);
+
+  GetStartupPerformanceTimes() => (StartupPerformanceTimes times);
+};